The process or method of the invention is a solution to the excessive cost of tooling and appalling waste of aluminum, steel, titanium, magnesium and other costly sheet metal generated by industry today. The process virtually eliminates expensive tooling (forming dies are not required), and it provides high-speed production with perfect repeatability in each process.
As later explained, machines of this character consist of two major units. The first is the forming unit through which flat sheets pass and emerge in a curved shape. The second is the power unit that grips one end of the sheet and pulls it through the working elements in the forming unit. The forming unit contains the elements with adjustable cams that provide a transverse curve for the elements. The power unit supports programmable traveling cams that transmit synchronized movement through sensitive electronic tracer controls to each element for positioning. Working together, the cams and elements produce the desired complex metal shape.
During the process, localized forces of a designed magnitude and direction are applied through the area and thickness of the metal sheet. The resulting continuous flow of infinitesimal forces results in a blended plastic formation of the metal virtually eliminating residual stress levels.
Techniques and appropriate machines of this character are described, for example, in Anderson U.S. Letters Pat. Nos. 2,395,651; 2,480,826; 2,851,080; 3,958,436; and other patents and prior art cited therein. Generally, such machines involve three stage functions--a sheet forming structure, a draw bench including a power actuated carriage for the mechanism, and a sheet pulling mechanism attached to and propelled by the carriage for gripping and drawing the sheet through the forming structure. That forming structure generally comprises three successive longitudinally spaced stages through which the sheet progressively moves.
In the first stage, a slot is defined by upper and lower relatively movable boundary surfaces having curvature-forming beads extending transversely across the sheet, with the upper and lower portions movable towards one another and from one another to engage the sheet and to be released therefrom with a restraining or constraining action provided as the sheet is bent about these beads, and which determines the general path of movement of the sheet. The next successive or second stage also has a slot that is formed by a draw-over forming element mounted usually on a vertical movable ram which, when closed to operating position, has its work-engaging face of different contours disposed in stepped (such as lower) relation to the entry slot of the second stage, actually to stretch and draw the sheet over the forming element, transversely across the sheet. The third stage also has a forming element, which may be of similar form to and contour of that of the second stage, also disposed in step relation so as to engage the side of the sheet that is opposite that engaged by the second stage forming element and serving to bring the contoured sheet along the direction of drawing. That drawing is effected by jaws or grippers that grip the head end of the sheet and, under control of the motor or some other power source, pull the sheet through the successive first, second and third stages to result in the compound curvature that is desired.
As more particularly explained in said U.S. Pat. No. 3,958,436, dynamic control of that forming with provision for responsiveness to the control mechanisms as sensed by contour monitoring sensors, enables control of the forming in accordance with such sensing during the drawing of the sheet through the stages. Such sensing of transverse physical dimension of lateral contour changes during the travel thus provides control signals for dynamically and electronically controlling the position of the forming elements at least relative to one another.
Generally, the first stage of transversely extending beads that bend and constrain the entering sheet material transversely across the sheet have involved double or multiple upper beads or ridges and corresponding parallel lower beads and valleys mating therewith which have been found necessary to provide the setting of the general path of movement of the sheet to the second drawing stage, particularly in the case of first stages that have substantially horizontal or flat bead structures. Where, for various compounding curves and materials, it is desired to introduce curvature, in a concave sense, transversely across the sheet in the first stage bead and slot, however, this structure does not provide the necessary flexibility for such purposes. It has been found, however, that a simpler single bead structure is then more workable. The double or other beaded boundaries of the first stage slot of the prior art, moreover, have been rearwardly provided with flat sections that move together with the contoured bead surface down onto the sheet in unison. As the bead starts to depress into the sheet material and bend the same for the desired path of travel to the second stage, the rearward flat portion is well above the sheet material, and the rearward portion thereof deflects upward and introduces instability into the operation, this being particularly so where the bead is formed into a curved structure transversely across the sheet.
This problem may be admirably solved by separating the rearward surface from the contoured or beaded part of the slot, independently moving it vertically downward to a predetermined clearance from the sheet. Under such circumstances, as the bead starts to depress into the sheet to bend it, the portion rearward thereof is not subject to the same deflection effects of the prior art construction.
While it has heretofore been proposed to curve the forming or constraining beads of the first stage, as for example on pages 50 to 52 of "Final Report on Effects of Andro forming on Material Properties" of the General Dynamics/Fort Worth Applied Manufacturing Research and Process Development Company for the U.S. Air Force, published November 1963, the provision of such radically modified bead contouring construction and the rearward surface independent adjustment to a predetermined gap clearance of the sheet have not heretofore apparently been discovered or known.
In such systems, the first stage bead or contoured constraining slot is positioned above the entry of the slot of the second stage and is generally transversely flat across the first stage. While this has been found to be useful for some thicknesses and strengths of sheet metal, this kind of operation has now been found to introduce wrinkles, ripples and other deleterious effects when relatively thin and sometimes composite metal surfaces and the like are employed, particularly metals and composites and alloys of quite different stress yielding points. This has also been found to be a disadvantageous method of operation for the above and other reasons where curvature transversely across the first stage is to be effected, as with concavely contoured first stage beads.